Electrochemical ion exchange with textured membranes and cartridge

ABSTRACT

An electrochemical cell  102  comprises an ion exchange membrane  10  having anion and cation exchange materials. The membrane  10  can have separate anion and cation exchange layers  12, 14  that define a heterogeneous water-splitting interface therebetween. In one version, the membrane  10  has a textured surface having a pattern of texture features  26  comprising spaced apart peaks  28  and valleys  30 . The membranes  10  can also have an integral spacer  80 . A cartridge  100  can be fabricated with a plurality of the membranes  10  for insertion in a housing  129  of the electrochemical cell  102 . The housing  129  can also have a detachable lid  96  that fits on the cartridge  100 . The electrochemical cell  102  can be part of an ion controlling apparatus  120.

BACKGROUND

Embodiments of the present invention relate to electrochemical ionexchange.

Ion exchange cells are used to remove or replace ions in solutions, forexample in the production of high purity water by deionization, in wastewater treatment, and in the selective substitution of ions in solution.Ion exchange materials include cation and anion exchange materials thatcontain replaceable ions or which chemically react with specific ions,to exchange cations or anions, respectively, from a solution stream. Atypical conventional ion exchange cell comprises ion exchange resinbeads packed into columns and a stream of solution to be treated ispassed through the column. Ions in the solution are removed or replacedby the ion exchange material, and product solution or waste emerges fromthe outlet of the column. When the ion exchange material is overwhelmedwith ions from the solution, the beads are regenerated with a suitablesolution. Cation exchange resins are commonly regenerated using acidicsolutions or salt brine (eg. for water softeners), and anion exchangeresins are most often regenerated with basic solutions or brine.

Another type of ion exchange uses a water-splitting ion exchangemembrane (also known as a bipolar, double, or laminar membrane)positioned between two facing electrodes with a dielectric spacerbetween the membranes, as for example, described in commonly assignedU.S. Pat. No. 5,788,826 (Nyberg) which is incorporated herein byreference in its entirety. The water splitting membranes have both acation exchange layer and an anion exchange layer. When a sufficientlyhigh electric field is applied through the membrane by applying avoltage to the two electrodes, water is irreversibly dissociated or“split” into component ions H⁺ and OH⁻ at the boundary between thecation and anion exchange layers. The resultant H⁺ and OH⁻ ions migrateand diffuse through the ion exchange layers in the direction of theelectrode having an opposite polarity (eg. H⁺ migrates to the negativeelectrode). During the regeneration step, the H⁺ and OH⁻ ions formed atthe membrane interface cause the rejection of cations and anions removedin a previous deionization step, reforming the acid and base forms ofthe cation and anion exchange materials. Electrical regeneration in thisway avoids the use, and subsequent disposal problems, of hazardouschemicals that are used to regenerate conventional ion exchange beads.

The ion exchange membranes of the prior art are typically smooth andflat, and also often have a uniform cross-sectional thickness, tominimize variations in current densities across the membranes inelectrochemical cells. Also a separate dielectric spacer, such as aplastic netting material, is typically placed between the membranes tomaintain the membranes at a uniform distance from one another to furtherreduce current density variation and maintain consistent mass transportrates and pressure drops across the gap between the membranes. Themembrane thickness is maintained uniform to provide a constant spacingbetween ion exchange membranes to generate uniform current densitiesacross membrane surfaces. Various methods can be used to maintain auniform thickness on the membrane. The membrane should also be flat andsmooth to facilitate the backwashing of ion exchange resins inelectrodeionization devices, and well as the periodic replacement ofthese resins. Membranes have a smooth flat surface also reduces thepressure drop between adjacent membranes. However, conventional ionexchange membranes generally provide slower ion exchange rates andconsequently, slower solution treatment flow rates and outputs, thanconventional ion exchange bead systems. Consequently, the membranesystems have limited utility due to space volume versus solutiontreatment throughout considerations.

Furthermore, the dielectric spacer layers that are used to separate themembranes in the electrochemical cells have to be sufficiently thick tobe free-standing and structurally sound to withstand handling wheninserted between the membranes in the fabrication of a cell. Typically,the spacer layers are fabricated from polymer, such as polyethylene orpolypropylene, and can have a regular pattern. A typical thickness ofthe spacer layer is from about 0.25 to about 1 mm (10 to 40 mils).Spacer layers thinner than 0.25 mm are difficult to handle and canresult in stretching of spacer strands, tearing or creasing, in theassembly of cells, and they are also generally more expensive anddifficult to make. A further problem in attempting to reduce spacerthickness arises because the pressure of the solution passed through thecell needs to be increased to deliver the same solution flow rate. Thus,generally, relatively thick spacer layers are used in theelectrochemical cell, further increasing the bulk volume of the cell andreducing solution treatment output per unit volume of cell space.

The stack of membranes and spacers is also difficult to assemble into orremove from the cell for cleaning or replacement. Typically, a number ofmembranes and spacers are used in a cell, and it is desirable to be ableto more easily handle the stack of membranes. The membrane stack canalso become easily disoriented in the cell during assembly of the cellor during use. Also, when membranes are sealed into water-tightelectrochemical cells, it is difficult to open the cells to remove themembranes without damaging the cell or membranes. A cell structure thatcan be easily assembled or opened is desirable.

Thus, it is desirable to have an electrochemical ion exchange cellcapable of providing good ion exchange rates. It is also desirable tohave a water-splitting membrane and spacer that exhibits sufficientstrength for handling and use and which is not excessively thick. It isfurther desirable to limit the number of steps needed to manufacturesuch cells, reduce the number of parts for assembly, and reduce assemblyerrors. It is also desirable to have a cell that can be easily assembledor disassembled without damaging or disorienting the membranes.

SUMMARY

A textured water-splitting membrane comprises an anion exchange layerabutting a cation exchange layer to form a heterogeneous water-splittinginterface therebetween and a textured surface having a pattern oftexture features comprising spaced apart peaks and valleys.

The membrane may also comprise an integral spacer on the texturedsurface. The integral spacer can be, for example, filaments on thetextured surface of the membrane or a coating on peaks of texturefeatures. The spacer separates the membranes from one another.

A cartridge for an ion exchanging electrochemical cell comprises aplurality of textured membranes abutting one another, each membranehaving (i) an anion exchange layer abutting a cation exchange layer toform a heterogeneous water-splitting interface therebetween, and (ii) atextured surface having a pattern of texture features comprising spacedapart peaks and valleys.

A method of manufacturing the cartridge comprises forming a plurality ofthe textured membranes, forming an offset membrane stack of texturedmembranes which are offset from one another, providing a core tube andwinding the offset membrane stack around the core tube to form acartridge roll, and attaching top and bottom end caps to the cartridgeroll.

For example, the offset membrane stack can be formed by laying themembranes on top of one another so that the top ends of the membranesare offset from one another in the same direction. The top ends of theoffset membranes are attached to one another. An outer sleeve canoptionally be wrapped around the cartridge roll to overlap itself:

A version of a housing for an electrochemical cell comprising acartridge having an end-cap extension with a flange, comprises, a vesselhaving a sidewall connected to a bottom wall, a solution inlet, and asolution outlet. A detachable lid that can be removably attached to thesidewall of the vessel is provided. The detachable lid comprises a platehaving a keyhole that extends therethrough. The keyhole has a first holehaving a dimension larger than the end-cap extension, and a second holewhich opens into the first hole and has a dimension smaller than theflange of the end-cap extension. In another version, the detachable lidof the vessel comprises a plate with a hollow post extending outwardlytherefrom, the hollow post sized to slide into or over the end-capextension of the cartridge of the electrochemical cell.

An electrochemical cell for removing or exchanging ions from a solutionstream comprises the cartridge, and a housing with first and secondelectrodes about the cartridge. The electrochemical cell can be formedby positioning the cartridge roll within a housing having solutioninlets and outlets so that the core tube is fluidly connected to asolution outlet of the housing. The electrochemical cell can be used inan electrochemical ion exchange system that also has a voltage supplyfor supplying a voltage to the first and second electrodes and a pumpfor flowing a solution stream through the electrochemical cell.

DRAWINGS

FIG. 1A is a schematic perspective view of a textured, water-splitting,ion exchange membrane with texture features that are a pattern of peaksand depressions and having an aspect ratio of approximately 1;

FIG. 1B is a schematic perspective view of another embodiment of the ionexchange membrane of FIG. 1A in which the aspect ratio is approximately0.5;

FIG. 1C is a schematic perspective view of another embodiment of the ionexchange membrane of FIG. 1A in which the boundary between the anion andcation exchange layers follows the contour of the textured surfaces toform a corrugated layer;

FIG. 1D is a schematic perspective view of another embodiment of the ionexchange membrane of FIG. 1A in which channels are cut across ridges andfurrows;

FIG. 1E is a schematic perspective view of another embodiment of the ionexchange membrane of FIG. 1A showing a dielectric coating on the ridges;

FIG. 2 is a schematic perspective view of another embodiment of the ionexchange membrane having texture features comprising conical protrusionsthat extend from a flat surface;

FIG. 3 is a schematic perspective view of another embodiment of the ionexchange membrane having texture features comprising mesas that extendout from a flat surface;

FIG. 4 is a schematic perspective view of another embodiment of the ionexchange membrane with an integral spacer of sprayed filaments formedover the texture features;

FIG. 5 is a schematic perspective view of an apparatus for forming thetextured membrane;

FIG. 6 is a schematic sectional top view of an electrochemical cellcomprising a cartridge having membranes with integral spacers that arespirally wound around a core tube;

FIG. 7 is a flowchart showing the steps involved in fabricated acartridge having spiral wound membranes;

FIG. 8A is a schematic perspective diagram showing a method ofassembling a stack of membranes;

FIG. 8B is a schematic perspective diagram showing glue lines on theassembled offset membrane stack and winding of the stack on a core tube;

FIG. 8C is a schematic perspective exploded diagram showing assembly ofan electrochemical cell having a housing, using the cartridge withrolled membranes, end caps, and a top plate;

FIG. 9A is a perspective exploded view of a detachable lid and cartridgeas the lid is being fitted to an end-cap extension of the cartridge;

FIG. 9B is a perspective view of the detachable lid and cartridge ofFIG. 9A after the lid is fitted onto the cartridge;

FIG. 9C is a schematic sectional side view of the detachable lid withattached cartridge of FIG. 9B fitted in a vessel;

FIG. 10A is a perspective exploded view of another version of adetachable lid and cartridge as the lid is being fitted to a core tubeof the cartridge;

FIG. 10B is a perspective view of the detachable lid and cartridge ofFIG. 10A after the lid is fitted onto the cartridge;

FIG. 10C is a schematic partial sectional side view of the detachablelid with attached cartridge of FIG. 10B fitted in a vessel;

FIG. 10D is a schematic partial sectional side view of a recessed groovein a sidewall of a vessel for receiving the pin of the lid of FIG. 10A;

FIG. 10E is a schematic partial sectional side view of a lid comprisinga post that extends into the core tube of a cartridge;

FIG. 11 is a schematic sectional view of an electrochemical cellcomprising a cartridge comprising membranes stacked in a plate and framecell; and

FIG. 12 is a schematic view of an ion controlling apparatus having anelectrochemical cell with a membrane cartridge and capable of providinga selected ion concentration in a solution stream.

DESCRIPTION

An electrochemical cell comprises an ion exchange membrane 10 (alsoknown as a bipolar, double, or laminar membrane), an exemplaryembodiment of which is shown in FIG. 1A. The ion exchange membranecomprises anion and cation exchange materials, which can be in the formof solids or gels, and contain ions which are replaceable by other ionsor ions which chemically react with specific ions to remove the ionsfrom a solution stream 20. For example, suitable cation and anionexchange materials can include cross-linked or un-cross linked organicpolymers or inorganic structures such as zeolites. Anion exchangematerials exchange anions with no permanent change to their structure,and can be for example, basic groups. Other suitable anion exchangematerials can include basic functional groups capable of exchanginganions such as —NR₃A, —NR₂HA, —PR₃A, —SR₂A, or C₅H₅NHA (pyridine), whereR is an alkyl, aryl, or other organic group and A is an anion (e.g.,hydroxide, bicarbonate, chloride, or sulfate ion). Cation exchangematerials exchange cations with no permanent change to the structure ofthe material, and can include, for example, acidic groups. Suitablecation exchange materials can include acidic functional groups capableof exchanging cations such as —COOM, —SO₃M, —PO₃M₂, and —C₆H₄OM, where Mis a cation (e.g., hydrogen, sodium, calcium, or copper ion). Cationexchange materials also include those comprising neutral groups orligands that bind cations through coordinate rather than electrostaticor ionic bonds (for example pyridine, phosphine and sulfide groups), andgroups comprising complexing or chelating groups (e.g., those derivedfrom aminophosphoric acid, aminocarboxylic acid and hydroxamic acid.

The selection of suitable cation and anion exchange materials for theion exchange membrane 10 depends on the application of the membrane. Inone version, the membrane 10 comprises an anion exchange layer 12abutting a cation exchange layer 14 to form a heterogeneouswater-splitting interface 18 having a boundary between the anionexchange layer 12 (or material) and the cation exchange layer 14 (ormaterial) which has continuous contact across the interface 18. Theanion exchange layer 12 contains anion exchange material and the cationexchange layer 14 contains cation exchange materials. For example, inthe deionization of a water based solution stream, the membrane 10 canhave an anion exchange layer 12 having —NR₃A groups such as triethylammonium (—N(C₂H₅)₃ groups, and an cation exchange layer 14 comprising—SO₃M or carboxylic acid (—COOH) groups. Such a membrane 10 swells inwater to have a lower electrical resistance and higher mass transportrate over a wide range of pH. Anion exchange materials comprising weakbase or weak acid groups are preferred when particularly efficient ionexchange regeneration is required. For example, —NR₂HA will react withOH⁻ in a very favorable reaction to form —NR₂, H₂O, and expel A⁻. Asanother example, for the selective removal of calcium or copper ionsfrom a liquid containing other ions, for example sodium ion, ionexchange groups such as —COOM or a chelating group such asaminocarboxylic acid are preferred. These weak acid groups offer theadditional benefit of particularly efficient regeneration due to thestrongly favorable reaction of —(COO)_(n)M with H⁺ to form —COOH andexpel M^(+n), where M is a metal ion.

Preferably, the membrane 10 is textured to have at least one exposedsurface 24 with texture features 26 comprising a pattern of repeatingthree-dimensional shapes, such as an array peaks 28 and valleys 30,exemplary embodiments of which are shown in FIGS. 1A to 1E, 2 and 3. Thetexture features 26 generally have dimensions that on the order ofmicrons or greater as explained below, and are not sized in sub-micronranges. In one version, the texture features 26 can have peaks 28 shapedlike ridges 36 a,b which are spaced apart and parallel to a flow path ofthe solution stream 20, and valleys 30 comprising furrows 38 a,b thatlie between adjacent ridges 36, as shown in FIG. 1A.

The ridges 36 a,b and furrows 38 a,b can be on both surfaces 24 a,b orlayers 12, 14 of the membrane 10. For example, in the version shown inFIG. 1B, the ridges 36 a,b and furrows 38 a,b are positioned on bothsides of the membrane 10 such that a ridge 36 a on one side (or layer)of the membrane 10 lies generally opposite a furrow 38 a on the otherside (or layer) of the membrane 10. This arrangement is better forproviding more uniform current density and hence better utilization ofion exchange capacity.

In yet another version, as shown in FIG. 1C, the entire membrane 10undulates with a furrow 38 a on the first surface 24 a following thecontour of a ridge 36 b on the second surface 24 b of the membrane 10,and a ridge 36 a on the first surface 24 a similarly following thecontour of the furrow 38 b on the second surface 24 b of the membrane10. In this version, the corrugated membrane 10 has a corrugationobtained from rows of ridges 28 running in the direction of the solutionstream 20 on both opposing sides of the membrane 10, i.e., the peaks 28a on one side of the membrane 10 lie opposite the valleys 30 b on theother side of the membrane 10. The corrugated membrane 10 provides auniform distance across anion and cation exchange layers 12, 14,respectively, in contrast to other membrane designs that can providethin and thick anion and/or cation layers as illustrated in 1B. Thisprovides still more uniform current densities and ion exchange capacityutilization. Other arrangements of the ridges 36 a,b and furrows 38 a,bcan also be used, for example, with the ridges 36 a and furrows 38 a onone surface 24 a asymmetrical to the ridges 36 b and furrows 38 b on theother surface 24 b, such that they are generally non-parallel or evenperpendicular to one another (not shown).

It may also be useful to texture only one side of a water-splittingmembrane 10, for example the surface 24 as shown in FIG. 1D, to increasethe extraction of either cations or anions. In this version, the surface24 a formed from the anion layer 12 has the ridges 36 and furrows 38,while the other surface 24 b is flat. This membrane 10 also has parallelridges 36 with channels 40 cutting across the ridges 36. The channels 40are oriented along a different direction than the orientation of theridges 36 (or furrows 38) to promote turbulence and/or increase surfacearea. For example, the channels 40 can be oriented generallyperpendicular to the orientation of the ridges 36 and furrows 38 so thatthey define additional passages that traverse the direction of flow ofthe solution stream 20 across the membrane 10. The channels 40 can alsobe oriented at any angular direction relative to that of the ridges 36or furrows 38.

The peaks 28 and valleys 30 of the texture features 26 can also be otherstructures other than ridges 36 and furrows 38. For example, the peaks28 can comprise conical protrusions 48 that extend out from an otherwisesubstantially flat surface region 49 which defines the valleys 30between the peaks 28, as shown in FIG. 2. In this version, the conicalprotrusions 48 are randomly spaced apart and distributed across themembrane surface. The conical protrusions 48 create a turbulentconvoluted flow of the solution stream 20 across the exposed surface 24of the membrane 10, which increases the residence time of the solutionstream 20 on the membrane 10. The conical protrusions 48 may be formedby abrasion, foaming, embossing, or any other suitable means. Instead ofa conical shape, the conical protrusions 48 can also have other shapesand dimensions.

In yet another version, the membrane 10 comprises texture features 26comprising peaks 28 shaped like mesas 50 that extend out of an otherwisesubstantially flat surface region 49 which defines the valleys 30between the peaks 28, as shown in FIG. 3. The mesas 50 have a flatcut-off top and are generally cylindrical with a rounded bottom edge.The mesas 50 can be formed, for example, impressing a mesh screen havinga pattern of round holes into a freshly formed membrane sheet by apress, such as a hydraulic press, or by running a membrane sheet throughrollers having a pattern of holes therein. This version is particularlyuseful when the solution stream has a large amount of dissolved solidsthat would otherwise get entrapped into the fine holes and spacesbetween other types of texture features 26.

It is believed that the texture features 26 on the exposed surface 24 ofthe membrane 10 can increase mass transport of ions between membrane 10and solution stream 20, and can also serve to separate the membranesfrom one another while still allowing solution to flow between membranesthrough texture valleys. In explaining the effects of texture on theexposed surface 24 of the membrane 10, it is beneficial to distinguishbetween geometric area, surface area, and surface roughness. Geometricarea is the area measured with a ruler when a membrane 10 is laid outflat on a planar surface. Surface area is measured on a scale thatincreases mass transport of species, e.g. ions, from solution to themembrane surface. The texture features 26 are provided to increase thesurface area for a given geometric area. The size of the texturefeatures 26 which must be considered in measuring surface area isdetermined by the solution stagnant layer thickness, which is typicallygreater than one micron as described below. Surface roughness refers tomicro-texture features 42, as described below, which are generallysub-micron sized features that are smaller than the solution stagnantlayer thickness, and hence do not substantially influence mass transportrates from solution to the membrane 10.

Thus, as certain dimensions of the texture features 26 increase, thesurface area of the exposed surface 24 of the membrane 10 alsoproportionately increases. If the dimensions of the textured features 26are greater than the stagnant layer thickness, mass transport rates intoand out of the membrane 10 will increase. The mass transport from asolution to a membrane 10 or other surface is proportional to thesurface area of the stagnant layer. At the boundary between a surfaceand a stirred or flowing solution there is a layer of solution, thestagnant layer, which is flowing or stirring at a significantly slowerrate than the bulk solution stream. The rate of flow is described interms of solution velocity that decreases as one nears the stagnantlayer from within the bulk solution, and this velocity is zero at thesurface. Because the solution velocity is a smooth continuous functionfrom the edge of the bulk solution to the immobile surface, the stagnantlayer thickness can be mathematically defined as the distance from thesurface at which the solution speed increases to 99% of the bulk orfreestream solution speed:Stagnant Layer Thickness, δ≅5/√Re _(x)  (2)where Re is the Reynolds number of the solution in the channel, andviscous flow dominates when Re is small (≦2000) and turbulent flowdominates when Re is large (≧2000). When the dimensions of the texturefeatures 26 are larger than the stagnant layer thickness δ, the stagnantlayer begins to follow the contour of the features 26 on the exposedsurface 24 of the membrane 10, and thus, the surface area of thestagnant layer increases with increasing membrane surface area. When thetexture features 26 have dimensions smaller than the stagnant layerthickness δ, the stagnant layer is essentially flat on the surface 24 ofthe membrane 10 to have a reduced surface area. Thus, for a givengeometric area, faster mass transport into and out of the cation andanion exchange layers 12, 14 of the membrane 10 results from increasingthe effective area of the stagnant layer by the use of features thathave dimensions greater than the stagnant layer thickness δ. Thetextured membranes 10 then has an effective surface area for masstransport that includes the larger area resulting from the convolutedtopography of the textured features 26. For the typical solutionvelocities of a solution stream passing across the surface 24 of amembrane 10, the stagnant layer thickness, δ, is usually about 1 micronor larger, with the layer thickness 6 increasing as the flow rate of thesolution stream decreases. Thus, a suitable dimension of the texturefeatures 26 of the membrane 10 should be at least about 1 micron, andmore typically at least about 10 microns.

As illustrated by the exemplary embodiments described above, the texturefeatures 26 have different shapes depending on their application, thatcan include for example, peaks 28 that are shaped as ridges 36, conicalprotrusions 48, or mesas 50; and valleys 30 formed by furrows 38,grooves 46 or flat surface regions 49. The dimensions of these peaks 28and valleys 30 can be appropriately described by, for example, peakheights or valley depths, the distance d_(pv) (peak to valley) whichwould be the distance from the crown 44 of a peak 28 to the base 52 of avalley 30, or d_(pp) (peak to peak) which would be the distance from onepeak 28 a to an adjacent peak 28 b. Referring to FIG. 2, the crowns 44of the peaks 28 are those portions of the peaks that are furthest fromthe water splitting interface 18 between the two ion exchange layers 12,14 of the membrane 10, and the base 52 of the valleys 30 are thoseportions of the valleys that are closest to the interface 18. Theabsolute dimensions selected depends on the application, since thinnermembranes 10 with texture features 26 having smaller dimensions providegreater surface area in a given volume of a cell, but may exhibitexcessive pressure drops due to the small channels available for flow ofthe solution stream between the features 26. In one version, the texturefeatures 26 comprise a distance d_(pv) of at least about 10 microns ormore preferably at least about 100 microns; and the distance d_(pp) canbe at least about 10 microns or more preferably at least about 100microns.

The texture features 26 of the membranes 10 can also be defined by anaspect ratio that depends on the balance of properties desired for anelectrochemical cell. Thus:Texture Feature Aspect Ratio=d _(pv) /d _(pp)  (1)In Equation 1, d_(pv) (distance peak to valley) refers to the averagedistance from a crown 44 x of a peak 28 x to a base 52 x of an adjacentvalley 30 x; and d_(pp) (distance peak to peak) refers to averagedistances between the crowns 44 x,y of the adjacent peaks 44 x,y. Forany given type of texture feature 26, such as the ridges, furrows,grooves, channels, or protrusions, the aspect ratios can be estimatedfrom average values for d_(pv) and d_(pp). The surface area of themembrane increases as the texture feature aspect ratio increases. Asuitable ratio of d_(pv)/d_(pp) is at least about 0.10, more preferablyat least 0.5, and most preferably at least 1.0. Excessively high aspectratios may provide a textured membrane 10 that folds or buckles duringassembly of the cell or high solution pressures and are thusundesirable.

A variety of methods may be used to fabricate the texture features 26 onthe water-splitting membrane 10. The selected fabrication method candepend upon the shape, dimensions, and spacing of the texture features26. For example, texture features 26 comprising peaks 28 that are shapedas parallel and spaced apart ridges 36 and valleys 30 shaped as furrows38 between the ridges 36, as shown in FIG. 1A, can be formed by passingan un-textured smooth membrane sheet 60 that is mounted as a roll 62 ona roller 64, through a pair of rollers 68 a,b, where at least one roller68 a has a imprinted roller surface 70 that is imprinted with the adesired pattern of circumferential raised portions 72 a andcircumferential troughs 72 b that correspond to the ridges 36 andfurrows 38, as shown in FIG. 5. When the smooth membrane sheet 60 passesthrough the pair of rollers 68 a,b, the imprinted pattern on the rollersurface 70 is embossed on the surface of the smooth membrane sheet 60that is in contact with the imprinted roller surface 70 to form atextured membrane 10 having a corresponding pattern of ridges 36 andfurrows 38. Other methods of forming the membrane 10 including, forexample, forming a pattern of mesas 50, as shown in FIG. 3, bythermoforming by compression the desired texture pattern on a smoothmembrane sheet 60 between plates or rollers. The pattern of conicalprotrusions 48 can be formed by sandblasting the membrane sheet 60,abrading the membrane sheet 60 with a stiff brush, or introducing openpores into the material of the membrane sheet 60 using foaming agents.Other methods capable of forming the texture features 26 on the membrane10 having peak-valley and peak-peak dimensions greater than the stagnantlayer thickness, for example, about 1 micron, are also suitable.

In another version, micro-texture features 42 are superimposed on top ofthe macro texture features 26, for example, fine grooves 74 that areabraded or scratched onto the peaks 28, as shown in FIG. 1D. In theversion shown, the fine grooves 74 are formed as a secondary pressedpattern onto the entire surface of the peaks 28. When the micro-texturedimensions are greater than the stagnant layer thickness, this increasesmass transport rates. Micro-texture features 42 comprising fine grooves74 that are abrasion marks can be formed on the membrane 10 by, forexample, sand blasting the membrane 10. The sand blasting can beperformed with a sequence of nozzles 75 mounted on a tube 76 that eachdirect abrasive particle jets 78 onto the membrane 10, as shown in FIG.5. The abrasive particle jets 78 can be forced out by pressured air orother gases. Suitable abrasive particles include aluminum oxide, siliconoxide, or silicon carbide. Pores or other fine texture features can beformed on the surface of the membrane 10 that is already coarselytextured with peaks 28 and valleys 30, for example, by adding a poreforming material to the membrane 10 during fabrication of the membrane10. The pore forming material can be dissolved out of the membrane 10during fabrication of the membrane 10 to form the pores on the membranesurface.

In another aspect of the invention, an integral spacer 80 providesspacing between adjacent membranes 10 to allow the solution stream 20 toflow across substantially all the exposed surfaces 24 of the membrane10. The integral spacer 80 is bonded to the textured membrane 10 to forma unitary article such that the membrane 10 and integral spacer 80 forma single structure. Advantageously, by being bonded to the membrane 10,the integral spacer 80 is not displaced from its position on themembrane 10 during the process of transporting the membrane 10 as rollsor sheets, or during the fabrication of cartridges or electrochemicalcells using the water-splitting membrane 10. The integral spacer 80 canbe adhered to either one or both of the exposed surfaces 24 a,b of themembrane 10. This integral spacer 80 should be formed of anon-conducting material, such as a dielectric material, that maintainsits shape in the solution to be treated. The thickness of the integralspacer 80 can vary over a wide range that depends upon the particularion removal application. For example, a thicker spacer 80 can provide astiffer membrane 10 which may not be useful for preparing a spiralwrapped cell design but which exhibits particularly low pressure dropeven at high flow rates. A thinner spacer 80 allows more concentriclayers of water-splitting membrane 10 to be wrapped in a given volume,thereby providing greater specific volume capacities. The spacer 80 hasa thickness which is sufficiently high to substantially prevent physicalcontact between adjacent membranes, which is typically at least about 10microns. The maximum spacer thickness, for practical reasons, is lessthan about 1000 microns. Spacer thickness greater than 1000 micronsreduce specific volume capacity with little benefit to reducing pressuredrops in most applications. It is also important to avoid blocking thevalleys 30 defined by the texture features 26 to allow the solutionstream 20 to flow substantially unrestricted across the exposed surface24 of membrane 10 and between the peaks 28.

The integral spacer 80 may be applied to the water splitting membrane 10by any method that provides spacing of adjacent membranes 10. Suitablemethods for applying the integral spacer 80 to the membrane 10 includespraying continuous polymer filament onto the texture surface 24 of themembrane 10, using a sprayer nozzle 86 that is connected via a feedtube88 to a polymer tank 85. The molten filament polymer is forced through afeedtube 88 by pressurized hot air from a tank 90 controlled by a feedvalve 92. Upon cooling the hot-sprayed filaments form an integralspacer, which is a randomly interspersed net of filaments. The polymertank 85 can contain an un-cured liquid polymer precursor or a moltenthermoplastic or thermoset polymer. Air temperature, air flow rate,distance from the membrane surface, and polymer softening temperatureare selected to form a desired thickness of the integral spacer 80 whileavoiding sagging of the hot polymer/fiber layer into the valleys 30 orother depressions of the textured features 26 formed on the exposedsurface 24 of the membrane 10—while providing good adhesion of theintegral spacer 80 to the membrane 10. In another method, filaments 82coated with a solution through which the textured membrane 10 is passed,can be applied onto the membrane 10 to form the integral spacer 80. Inyet another method, gravure coating of the crowns 44 of the peaks 28 ofthe texture features 42 can also be used to form the integral spacer 80.The integral spacer 80 can also be fabricated by methods, such as forexample, those used for the preparation of non-woven fabrics. While thetextured membranes 10 may have only one textured surface, to obtainuniform flow of the solution stream across both membrane surfaces 24a,b, it can be preferred to employ textured membranes 10 that havesurface texturing on both surfaces for use of the integral spacer 80;otherwise, a spacer 80 laying flat against a membrane surface can blockthe flow of a solution stream or cause the solution to preferentiallyflow past a textured surface 24 a and potentially preventing it fromefficiently flowing across opposing or adjacent flat surface 24 b of amembrane 10.

The integral spacer 80 between the membranes 10 provides a significantreduction in volume of an electrochemical cell 102. Conventional spacerlayers, while they can still be used, have to be sufficiently thick tobe freestanding and structurally sound to withstand handling wheninserted between the textured membranes 10 in the fabrication of a cell102. Typically, conventional spacer layers are fabricated from polymer,such as polyethylene or polypropylene, and have a thickness of fromabout 0.25 to about 1 mm. Spacer layers thinner than 0.25 mm aredifficult to handle and can result in stretching of spacer strands,tearing or creasing, in the assembly of cells, and they are alsogenerally more difficult to make. A further problem in attempting toreduce spacer thickness arises because the pressure of the solutionpassed through the cell needs to be increased to deliver the samesolution flow rate. Thus, conventionally, relatively thick spacer layersare used in a cell 102, which increases the bulk volume of the cell andreduces solution treatment output per unit volume of cell space.However, conventional spacer layers can still be used with the texturedmembranes 10 to provide effective electrochemical cells 102, especiallywhen space and cell volume is not of primary concern, or for example,when the space between the membranes 10 needs to be larger than thatprovided by the integral spacers 80.

The textured membranes 10 and optional integral spacers 80, or separatespacer layers, are assembled into a cartridge 100 that facilitatesinstallation and removal of the membranes 10 from an electrochemicalcell 102, embodiments of which are shown in FIGS. 6 and 7. The cartridge100 can be easily removed from the cell 102, which may be necessary whenthe space between the adjacent pairs of membranes 10 and their integralspacers 80 become clogged, for example, with calcium carbonate scale orother solid materials. The cartridge 100 also facilitates shipment ofreplacement membranes 10 to the distributor or end user. In addition,the cartridge 100 also allows a particular membrane configuration thatpromotes efficient ion exchange to be fabricated.

In one embodiment, the cartridge 100 comprises several membranes 10 withintegral spacers 80 that are spirally wound around a core tube 106,which is typically cylindrical, as shown in FIG. 6. The spirally woundmembranes 10 can be enclosed by an outer sleeve 110, and sealed at bothends with two end caps 114 a,b. When the membrane 10 does not have anintegral spacer 80, the cartridge 100 is fabricated with a spacer sleeve(not shown) between each membrane 10, as for example, described incommonly assigned U.S. patent application Ser. No. 10/637,186, filed onAug. 8, 2003, entitled “Selectable Ion Concentration with ElectrolyticIon Exchange,” which is incorporated herein by reference in itsentirety. The surfaces of the outer sleeve 110, core tube 106 and endcaps 114 a,b direct the solution stream 20 through a solution passageway115 that passes across the exposed surfaces 24 of the textured membrane10 in traveling from the inlet 116 to the outlet 118 of the cell 102.The cartridge 100 may be designed for a variety of flow patterns, forexample end-to-end flow (parallel to the cored tube 106) orinner-to-outer flow (radial flow to or from the core tube 106).

Each end cap 114 a,b of the cartridge 100 can be a flat plate mounted oneither end of the core tube 106. The core tube 106, outer sleeve 110 andend-caps 114 a,b are designed to provide a solution passageway 115 thatprovides the desired flow pattern across substantially the entiremembrane surface. For example, for the solution stream 20 to flowradially to or from the core tube 106, across both the inner and outersurfaces of each textured membrane 10, the end-caps 114 a,b seal theends of the spirally wound membrane to prevent solution from by-passingthe membrane surface on its way from inlet to outlet. The texturedmembranes 10 can also be arranged in the cartridge 100 to provide asolution passageway 115 that forms a unitary and contiguous solutionchannel that flows past both the anion and cation exchange layers 12, 14of each membrane 10. Preferably, the unitary channel is connectedthroughout in an unbroken sequence extending continuously from the inlet116 to the outlet 118, and flowing past each anion and cation exchangelayers 12, 14, respectively, of the water-splitting membranes 10. Thusthe unitary and contiguous channel's perimeter comprises at least aportion of all the cation and anion exchange layers 12, 14, of themembranes 10 within the cartridge 100.

The membranes 10 can be spiral wrapped with the integral spacers 80formed on the inner surface of a cation exchange layer 14 separating itfrom the adjacent anion exchange layer 12, and providing the solutionpassageway 115 therebetween. In this one embodiment, three membranes 10are spiral wrapped to form a parallel flow arrangement, which means thatthe solution can flow from inlet to outlet in three equivalentpassageways between membrane layers. For any flow pattern, for exampleparallel or radial relative to the core tube 106, one or more membranes10 can be wrapped in a parallel arrangement to vary the pressure dropacross the cartridge 100, the number of membranes 10 that are beingwrapped in a parallel flow arrangement selected to provide the desiredpressure drop through the cell 102. While the membranes 10 are generallytightly wound against each other, for pictorial clarity, the membranes10 are shown loosely wound with spaces between them. In this version,the wrapped cartridge 100 is absent electrodes, which are positionedoutside the cartridge in the cell.

One cartridge fabrication method, as illustrated in the flowchart ofFIG. 7, reduces the time and labor required to fabricate a cartridge 100having spiral wound membranes 10. In this method, the cartridge 100 isfabricated from a plurality of membranes 10, for example, from about 2to about 100 membranes. In one version, six textured membranes 10 a-fare wrapped in a parallel flow arrangement. The parallel flowarrangement allows the influent solution stream 20 which is passed intothe cartridge 100 to flow simultaneously through a number of parallelflow paths, each of which lies between parallel membranes 10. Themembranes 10 a-f are laid up one on top of the other, on a flat tablesurface, with the top ends 113 a-f of the membranes 10 offset from oneanother, as shown in FIG. 8A. In one version, the top ends 113 a-f ofthe membranes 10 a-f are offset by a distance d_(o)=3.14*d_(c)/n, whered_(c) is the outer diameter of the core tube 106 on which the membranes10 a-f are wrapped. Offsetting membranes ensures that the top ends 113a-f of the membranes 10 a-f contact the core tube 106 to provide inletsor entrances in the gaps between the membranes 10 a-f for fluid to enterbetween and flow through all membranes. If membranes 10 a-f are notoffset, the flow of fluid may be constricted to some of the membranes 10a-f, thereby reducing cartridge performance. It is not necessary toevenly space all the membranes 10 a-f apart by the distance d_(o), butthe top ends 113 a-f should be offset in the same direction, and shouldbe arranged so that all the membranes fall within the circumference ofthe core tube 106. Evenly spacing apart the top ends 113 a-f of themembranes 10 a-f while forming the assembly provides more uniform flowinto and out of the cartridge to provide more thorough replacement ofsolution in the inner and outer cell volume.

The assembled of membranes 10 a-f are then attached to one other to forman assembled offset membrane stack 119. The membranes 10 a-f can beattached by, for example, clips, glue, heat staking, rivets, sewing,staples, ultrasonic bonding or welding. In a preferred method ofattachment, the stack 119 of membranes 10 a-f is attached to the coretube 106 by glue, such as Macromelt Q5353 or Technomelt Q5305, both fromHenkel. For drinking water applications, glue should meet extractionrequirements of FDA 21 CFR 175.105. In a preferred version, the glue isdispensed from a multi-head applicator to apply narrow lines or zigzaglines of glue crossing the top ends 113 a-f of all the n membranes 10a-f to bond only the ends of the membranes, as shown in FIG. 8B. Thisgluing method assures the membranes 10 a-f can slide across one anotherwhen subsequently wound around the core net tube to avoid a lump whenwinding the assembled stack on a core tube 106.

The top surface 123 of the first membrane 10 a of the assembled stack 10a-f is then positioned on the core tube 106 so that the top ends 113 a-fare closest to the tube. The stack 119 may be attached to the core tube106 by applying a glue line on the edge of the top surface of the bottommembrane 10 a of the stack 119. The stack 119 is then wound around thecore tube 106 while applying a pressure to the membranes 110 to producea wound cartridge 100. During winding, the stack 119 can be maintainedunder tensile or compressive strain by applying a compressive force onthe stack 119 as it is being wound around the core tube 106 for exampleby squeezing the stack 119 with for example one or more rolls.Alternatively, the opposing bottom ends 117 a-f of the membranes 10 a-fcan also be pulled out to maintain the membranes under tension while thestack 119 is being wound around the core tube 106.

Sub-assemblies of membranes 10 which contain less than the total numbern of membranes desired in the cartridge can also be used to reduce thenumber of objects required to assemble a cartridge 100. For example, twoor more sub-assembly stacks of membranes can be stacked and themembranes attached to each other as described above, each sub-assemblycomprising n/x sheets (not shown), where n is the total number ofdesirable sheets, and x is the number of sub-assemblies. The xsub-assembly stacks may then separately attached to the core tube 106,or attached to each other prior to attachment to the core net tube. Thisprocedure again allows the individual membranes 10 to slide across eachother during winding rather than bunching up to form a lump adjacent tothe surface of the core tube during the membrane winding process. Anybunched up membrane lumps would interfere with the flow of fluid throughthe cell 102 and also increases the diameter of the finished cartridge100.

In another version, the top or bottom ends of the membranes 10 areattached to an outer sleeve 100 to provide a stronger assembly. Theouter sleeve 110 can be a porous sheet, such as a spacer net made from adielectric, or hydraulically permeable, material such as for exampleUltraflow 3725 netting from Delstar, Tex. The spacer net comprises anetwork of holes 133 which allow solution to permeate into the rolledstack of membranes. For example, the outer sleeve 110 can have holeshaving dimensions, such as a width and height or a diameter, sized fromabout 0.1 to about 10 mm. The attachment to the sleeve 110 provides astronger assembly if using fragile or heavier membranes.

In one version, the outer sleeve 110 is attached to the bottom end 135of one of the upper membranes 10 d, as for example shown in FIG. 8B,which is opposite to the top end 113 d which is first wound on the coretube 106. The sleeve 110 serves as a containment wrap to contain themembranes 10 which are wound on the core tube 106 to form the cartridge100. The sleeve 110 is attached to membrane 10 d with a line or spots ofglue, or other means. The sleeve 110 has a length that is sufficientlylong to wrap completely the wound; stacked membranes until it overlapson itself, forming a porous sheet tube around the spiral woundmembranes. The sleeve 110 may then attached to itself with glue, a weld,a fiber, or other means to enclose the stack 119 to form an assembledcartridge roll 136 as shown in FIG. 8C. After fabrication, the cartridgeroll 136 is cut to the desired length to fit into a housing 129 of anelectrochemical cell 102. The top and bottom end caps 114 a,b are thenpositioned on the ends of the cartridge roll 136 and are also glued tothe roll 136 to form the assembled cartridge 100. Each end cap 114 a,bhas a hole 133 a,b to allow fluid to enter the core tube 106.

The cartridge 100 is positioned within a housing 129 of theelectrochemical cell 102. The housing 128 is typically, but notnecessarily, a cylinder made of a polymer, which is non-conductive,resistant to hydrolysis in water, acids and bases, having goodstructural properties. Suitable polymers for the housing include, forexample, polyvinylchloride (PVC), CPVC, polypropylene, or NORYL™,General Electric, New York. The housing can be fabricated by injectionmolding or other means. The housing 129 has through-holes that serve asa solution inlet 116 for introducing an influent solution stream 20 intothe cell 102 and a solution outlet 118 to provide an effluent solutionstream. The housing 129 typically comprises two or more sections, forexample, a vessel 93 comprising a tubular sidewall 94 with a bottom wall95, and a detachable lid 96 which fits onto the vessel sidewall 94. Thecartridge 100 is slid into the housing 129 so that the core tube 106 ofthe cartridge 100 slides over through-hole in the housing 129 to formthe solution outlet 118 in the housing 129. Typically, the solutionoutlet 118 is positioned at the center of a bottom surface 145 of thehousing so that the hole 133 b in the bottom end cap 114 b can fluidlyconnect to the solution outlet 118. The solution outlet 118 can be ahole as shown or a short cylinder (not shown) that protrudes out toslide into the hole 133 of the core tube 106. O-ring seals and gasketscan be used to seal the hole 133. Advantageously, the cartridge 100 canbe easily removed for cleaning or replaced from the housing 129. A topplate 147 is then used to cover up the other end of the housing 129.

Additional layers such as the outer electrode 124, electrode support,etc., as shown in FIG. 6, are also placed between the cartridge 100 andthe housing 129. For example, the outer electrode 124 and centralelectrode 128 are in the housing 129 such that the cation exchangelayers 14 of the membranes 10 face the first electrode 124, and theanion exchange layers 12 of the membranes 10 face the second electrode128. The electrodes 124, 128 are fabricated from electrically conductivematerials, such as metals, which are preferably resistant to corrosionin the low or high pH chemical environments created during positive andnegative polarization of the electrodes during operation of the cell102. Suitable electrodes 124, 128 can be fabricated fromcorrosion-resistant materials such as titanium or niobium, and can havean outer coating of a noble metal, such as platinum. The shape of theelectrodes 124, 128 depends upon the design of the electrochemical cell102 and the conductivity of the solution stream 20 flowing through thecell 102. Suitable electrodes 124, 128 comprise a wire arranged toprovide a uniform voltage across the cartridge. However, the electrodes124, 128 can also have other shapes, such as cylindrical, plate, spiral,disc, or even conical shapes. In this version, the core tube 106 alsoserves as the inner electrode 124.

In one version, as shown in FIGS. 9A and 9B, the housing comprises adetachable lid 96 that slides over and holds the cartridge 100 duringassembly of the cell 102. The detachable lid 96 comprises a plate 97with a side surface 98 having an external male thread 99 for screwinginto a receiving female thread 136 in the housing 129 of the cell 102,and a handle 137 which assists an operator in screwing in and out thelid 96. The detachable lid 96 further comprises a keyhole 140 thatextends thorough the plate 97 to receive an end-cap extension 143 (whichis a protruding portion of the top end-cap 114 a) which extends out ofthe top of the lid 96. The top cartridge cap comprises an o-ring on itsperiphery, which forms the seal to the housing when fully inserted. Thelid 96 holds the cartridge in position when under pressure. The end-capextension 143 further comprises a flange 148, which extends outward fromthe distal end of the extension. The keyhole 140 comprises a first hole146 having a dimension larger than the flange 148 of the end-capextension 143 so that the extension 143 with its flange 148 can slidethrough the hole 146. When the end-cap extension 143 is circular, thefirst hole 146 has a diameter larger than the diameter of the end-capextension 143, for example, by about 5% or more. The first hole 146opens to a second hole 149, which can be shaped as elongated apertureending in a semicircular contour, which has a dimension, sized smallerthan the dimension of the flange 148 to snugly fit about the circularperimeter of the extension 143. To assemble the cell 102, an operatorinserts slides the first larger hole 146 of the keyhole 140 of thedetachable lid 96 over the flange 148 of the end-cap extension 143, asshown in FIG. 9A. Then the lid 96 is slid forward so that the end-capextension 143 passes into the smaller second hole 149 of the keyhole, asshown in FIG. 9B. Now, the lid 96 can be screwed onto the sidewall 94 ofthe vessel 93 with the cartridge 100 firmly attached to the lid 96because the flange 148 holds the cartridge 100 to the lid 94. Acompleted version of the lid 96 with attached cartridge 100, which isscrewed onto a vessel, is shown in FIG. 9C.

In still another version, as shown in FIGS. 10A and 10B, the detachablelid 96 also comprises a plate 97 with a side surface 98 having at leasta pair of outwardly projecting pins 152 that slide into a recessedgroove 154 in the sidewall 94 of the vessel 93 to lock into place.However, in this version, a short hollow post 156 extends out of theplate 97. In one version, the hollow post 156 extends downwardly fromthe bottom surface 91 of the plate 97 and is sized to slide over the endcap extension 143 in the direction of the arrow, as shown in FIG. 10A;and in this version, the post 156 has an inner diameter sized to snuglyfit over the outer diameter of the extension 143, the inner diameter ofthe post 156 being sized about 2% or so larger than the outer diameterof the extension 143. In another version, the hollow post 156 extendsupwardly from the top of the plate 97, as shown in FIG. 10C. In yetanother version, the hollow post 156 is sized to slide into the end-capextension 143, as shown in FIG. 10E, and in this version, the hollowpost 156 has a dimension such as an outer diameter that is smaller thanthe inner diameter of the end-cap extension 143 to fit snugly into theextension. The snug fit is used to hold the cartridge 100 to the lid 96while the lid 96 is locked into place in the sidewall 94 of the vessel93 and rotated to engage the pins 152 into the recessed groove 154 toform a tight seal. The groove 154 can also have a sloped portion 101with a step-down locking channel 105, as shown in FIG. 10D, so that thelid 96 can be pushed down and rotated into the step-down locking channel105 to lock the lid 96 into the vessel 93. Also, a recessed first groove158 can be positioned about the base of the hollow post 156 to hold anO-ring seal 160 which fits into a corresponding second groove 162 on thetop surface of the core tube 106 to form a more water tight seal for thehollow post 156, as shown in FIG. 10A. The seal is provided by an O-ringon the periphery of the end-cap 114 a.

The cell 102 can also have other embodiments, such as for example, aplate and frame configuration, as shown in FIG. 11. In this embodiment,the electrochemical cell 102 comprises a cartridge 100 having a numberof textured membranes 10 a-g having a rectangular shape, which arestacked on top of one another and attached to the sidewalls 122 of thecell to form an interdigited arrangement. The membranes 10 a-g areseparated by gaskets 104 and spacers 108 between pairs of adjacentmembranes. Openings 121 are punched into one end of each membrane 10 a-gjust inside the outline of the gasket 104, and the membranes 10 a-g arepositioned such that the openings are positioned on alternating ends ofthe stack to form unitary and continuous solution passageway 115 throughthe cartridge 100. The gaskets 104 are flexible to prevent leakage ofthe solution through the sidewalls 122 of the cartridge 100, and aremade of an electrically insulating material to prevent shorting ordivergence of the electrical current channel through the sidewalls 122.This forces the electrical current channel, or the electrical fieldbetween the electrodes 124, 128 to be directed substantiallyperpendicularly through the plane of the membranes 10 a-g to providemore efficient ion removal or replacement. The spacers 108 may beintegral spacers (not shown) or separable spacers 108 (as shown) such asnetting made from a dielectric material, such as plastic. The spacers108 separate the membranes 10 a-g to provide more uniform solution flowand create turbulence in the solution stream passageway 115 to providehigher ion transport rates. Two electrodes 124, 128 comprising, forexample, plates of titanium coated with noble metal catalyst arepositioned on either end of the stacked membranes 10 a-g. Rigid plates125, 126, made from plastic, are placed over the electrodes 124, 128.The electrodes 124, 128, membranes 10 a-g, and gaskets 104, arecompressed using metal bolts 127 a,b passing through the edges of therigid plates 125, 126 which extended beyond the edge of themembrane/gasket/electrode stack. The bolts 127 a,b are tightened withthe nuts 131 a-d at the ends of the bolts. Electrical connections aremade to terminals 132 a,b of the electrodes. This embodiment isadvantageous when uniform current density across all the membranes 10a-g is required. This cell design with integral spacers also allowshigher ion removal or replacement rates due to the larger total surfacearea of membrane 10 a-g in contact with the solution stream 20, while atthe same time allowing the treatment of greater volumes of solution dueto the larger ion exchange capacity.

FIG. 12 presents an embodiment of an ion controlling apparatus 20 toprovide a selected ion concentration in a product stream using anelectrochemical cell housing a cartridge. A pump 130 can be used to pumpthe solution stream through the cell 102, such as a peristaltic pump orwater pressure from the city water supply in combination with a flowcontrol device. A power supply 134 powers the first and secondelectrodes 124, 128. The power supply 134 can be capable of maintainingthe first and second electrodes 124, 128 at a single voltage, or aplurality of voltage levels during an ion exchange stage. The powersupply 134 can be a variable direct voltage supply or a phase controlvoltage supply as described in aforementioned patent application Ser.No. 10/637,186. In one version, the power supply 134 comprises avariable voltage supply that provides a time modulated or pulsed directcurrent (DC) voltage having a single polarity that remains eitherpositive or negative, during an ion removal step, or during an ionrejection step. In contrast, a non-DC voltage such as an alternatingcurrent (AC) supply voltage has a time-averaged AC voltage that would beapproximately zero. Employing one polarity over the course of either anion removal (deionization) or ion rejection (regeneration) step in theoperation of the electrolytic ion exchange cell 102 allows ions in thesolution 20 being treated to travel in a single direction toward or awayfrom one of the electrodes 124, 128, thereby providing a net masstransport of ions either into or out of the water-splitting membranes10. The magnitude of the average DC voltage is obtained bymathematically integrating the voltage over a time period and thendividing the integral by the time period. The polarity of theintegration tells whether one is in ion removal or rejection mode, andthe magnitude of this calculation is proportional to the electricalenergy made available for ion removal or rejection.

An output ion sensor 144 can also be positioned in the solution streamexterior to the outlet 118 (as shown) or interior to the housing 129 todetermine the ion concentration of the treated solution. The ion sensor144 can measure, for example, concentration, species, or ratio ofconcentrations of ions in the treated solution. In one version, the ionsensor 144 is a conductivity sensor, which is useful to determine andcontrol total dissolved solids (TDS) concentration in the treatedeffluent solution 20. Alternatively, the ion sensor 144 can be a sensorspecific to a particular ionic species, for example nitrate, arsenic orlead. The ion specific sensor can be, for example, ISE (ion selectiveelectrode). Generally, it is preferred to place the ion sensor 144 asfar upstream as possible to obtain the earliest measurement. The earlierthe ion sensor measurement can be determined in this embodiment, themore precisely can be controlled the ion concentration of the treatedsolution.

A controller 138 can operate the power supply 134 in response to an ionconcentration signal received from the ion sensor 144 via a closedcontrol feedback loop 142. The controller 138 is any device capable ofreceiving, processing and forwarding the ion sensor signal to the powersupply 134 in order to adjust the voltage level, such as for example, ageneral purpose computer having a CPU, memory, input devices anddisplay—or even a hardware controller with suitable circuitry. In oneversion, the controller sends a control signal to the power supply 134to control the voltage output to the electrodes 124, 128. The controller138 comprises electronic circuitry and program code to receive,evaluate, and send signals. For example, the controller can comprise (i)a programmable integrated circuit chip or a central processing unit(CPU), (ii) random access memory and stored memory, (iii) peripheralinput and output devices such as keyboards and displays, and (iv)hardware interface boards comprising analog, digital input and outputboards, and communication boards. The controller can also compriseprogram code instructions stored in the memory that is capable ofcontrolling and monitoring the electrochemical cell 102, ion sensor 144,and power supply 134. The program code may be written in anyconventional computer programming language. Suitable program code isentered into single or multiple files using a conventional text editorand stored or embodied in the memory. If the entered code text is in ahigh level language, the code is compiled, and the resultant compilercode is then linked with an object code of pre-compiled libraryroutines. To execute the linked, compiled object code, the user invokesthe object code, causing the CPU to read and execute the code to performthe tasks identified in the program. An electrochemical cell 102 havingthe textured membranes 10, and optional integral spacer 80 overlying themembrane 10, provides better control of the ion composition of thetreated solution stream, in comparison with conventional electrochemicalcells, and the ion concentration in the treated solution stream can befurther improved by closed loop control system.

One method of comparing the ion exchange results from a conventionalcell having un-textured membranes to the results obtained from a cell102 having textured membranes 10, is the power law equation provided asEquation (3). In this equation, L is the fraction of ions left insolution after passing over N segments of the textured membrane 10 eachhaving a geometric area A. Thus if membrane segment A leaves 50% of ionsin solution, then two sequential membrane segments A will leaveA²=0.5²=0.25 or 25% of ions in solution (for a TDS reduction of 75%).The key is to measure the value of A from an experiment underwell-defined and consistent regeneration and deionization conditions(including volume of water deionized).L=A^(N)  (3)Equation (3) allows normalization of results for cells 102 that eachhaving different total membrane areas and/or different membranes. Forexample, assuming that a first cell has a total membrane area of 0.070m²; to use Equation 3, one must first define an area A, which will beconsistently applied for all calculations and comparisons, for example,let A=0.1 m² (it can be any value). For a cell according to thisexample, N=0.70 (the actual cell is 0.070 m², so it contains 0.7 unitsof the defined membrane area A). The ion removal or replacementexperiment is completed under specified conditions, including volume ofsolution deionized, which for this example is 1 liter. The experimentmeasures L, the fraction of ions left in the treated solution. Assumethat L=0.6 (60% ions left in solution) for this cell, N=0.70, then onecalculates A=0.482. Now one can determine the liters of challenge waterthat can be treated to any TDS reduction level, for this example say 90%reduction by 1 m² of this membrane (where 90% TDS reduction and the onesquare meter serve as the normalization factors). Let L=0.1, A=0.482,and ones calculates N=3.16. Thus the geometric area of membrane to treat1 liter of water to 90% TDS reduction is 0.316 m²; and the liters ofwater which can be reduced by 90% TDS reduction under the specifiedconditions is 3.16 liters/m². One can then compare various membranes,textured and untextured, by the volume of water that can be treated to90% TDS reduction, as an example, per 1 m² membrane.

EXAMPLES

The following examples demonstrate the effectiveness of the ioncontrolling apparatus 120, electrochemical cell 102, and membranes 10fabricated according to the present invention. In these examples,membranes 10 were fabricated by different methods and their ion exchangeperformance in electrochemical cells evaluated for comparisons.

Examples 1 and 2

These examples were performed to compare the performance of aconventional first electrochemical cell having un-textured membranes tothe performance of a second electrochemical cell 102 fabricated withtextured membranes 10. In both types of cells, the membranes were madeby laminating together a pair of cation and anion exchange layers. Thecation exchange layer was made from a mixture of 72 wt % strong acid ionexchange resin powder with the tradename CG8-PWD available fromResintech, mixed with a polyethylene binder, such as SLX 9090 fromExxon. The anion exchange layer 12 was made from a mixture of 65 wt %strong base ion exchange resin powder with the tradename SBG1P-PWD, alsoavailable from Resintech and the same polyethylene binder. The anion andcation exchange materials were each separately mixed on a Banbury mixer.Each of the mixed compositions were then separately pressed into slabs,swollen in water, then cut into the 7 by 14 cm pieces. Pairs of anionand cation exchange slabs were laid on top of each other to form amembrane sheet.

In Example 1, a conventional electrochemical first cell, similar to theone shown in FIG. 7, was built using a plate and frame construction.Seven un-textured (flat) water swollen membrane sheets, each about 2 mmthick provided a total geometric area of about 0.0702 m². Holes werepunched into one end of each membrane sheets at the corners just insidethe gasket outline, and the membrane sheets were stacked on one anotherwith the holes positioned on alternating ends of the stack to build aplate and frame cell. The membrane sheets were separated by rubbergaskets (1 mm thick) with dielectric netting (also 1 mm thick) toprevent membranes from contacting one another.

Two electrodes each comprising a contiguous sheet titanium coated with aproprietary noble metal catalyst, referred to as DSA electrode,available from Electrode Corporation were positioned on the two ends ofstack. This stack was placed between two rigid plastic plates sized 17cm by 10 cm and 2.5 cm thick. The plates, membranes and gaskets werecompressed using metal bolts passing through the edges of the plates.Electrical connections were made between the electrodes and washersmounted on the outside of the plastic plates using metal springs.

A power supply was used to supply a current to the electrodes of thefirst cell that was limited to no more than 240 mA at a voltage of 120V. The cell was then regenerated with water having a conductivity of 60uS/cm at 20 ml/minute for a total of 30 minutes. A water solution streamcomprising 380 ml of a 750 ppm NaCl (having a conductivity of 1550uS/cm) at a flow rate of 50 ml/minute was deionized in the cell. Thetotal dissolved solids (TDS) removed from the treated solution from thefirst cell was measured as 89%. Using the power law normalizationtechnique to calculate the volume of water each square meter of membranetreated under these flow and power conditions to provide 90% R, oneobtains 4.7 liters/m² geometric membrane area for this deionizationvolume with the recited regeneration and deionization conditions usingun-textured membrane.

In Example 2, a second electrochemical cell 102 was fabricated withtextured membranes 10 fabricated by embossing the dry, flatwater-splitting membrane sheets used for Example 1. Pairs of cation andanion exchange slabs were pressed between two rigid, metal texturedplates in a hot press to form texture features 26 shaped as parallel,spaced apart, ridges 36 and furrows 38, on both sides of the membrane10, and running parallel to the direction that the solution stream wouldrun across the membrane. The texture features 26 had d_(pv) (peak tovalley) dimensions of about 0.08 cm and d_(pp) (peak to peak) dimensionsof 0.15 cm. These textured membranes 10 were swollen in water and cutinto seven 7 cm by 14 cm slabs, providing a total geometric area ofabout 0.0702 m². Cell construction and operation were provided as inExample 1. This second cell 102 provided a TDS reduction of 95% for thesame 0.38 liters of 750 ppm NaCl deionized in the cell; this equates to6.8-liters/m² membrane for 90% TDS reduction when using these texturedmembranes.

Thus, the second cell 102 of Example 2 having textured membranesprovided a 45% improvement in membrane performance as compared with thefirst cell of Example 1 which had un-textured membranes. Thisrepresented a significant and unexpected improvement in membraneperformance for the same geometric area of membranes and processconditions.

Examples 3 and 4

In these examples, the performance of a cell having spirally woundun-textured membranes was compared to a cell 102 having spirally woundtextured membranes 10. In both cells, the membranes 10 were fabricatedfrom a cation exchange layer 14 made from a blend of 60 wt % strong acidion exchange resin powder (CG8-PWD; from Resintech) and 40 wt %polyethylene (SLX-9090; from Exxon), and an anion exchange layer 12 madefrom 65 wt % anion exchange resin powder (SBG1P-PWD; Resintech) and 34wt % of the polyethylene. The ion exchange resin powders are <150 um andcomprise <2% water. The cation and anion exchange materials were eachmixed on a Banbury mixer taking care not to thermally degrade the ionexchange resins. Membrane sheets were formed by sheet extrusion using a25.4 cm wide extrusion die. The cation exchange layer was extruded firstto form a 0.025 cm thick sheet, and the anion exchange layer extruded ontop of this to produce a water-splitting membrane. A second calendaringstep using the extrusion roll stack was employed to thin the sheet to0.028 cm thick, and upon swelling in water the flat water-splittingmembrane sheet was about 0.038 cm thick.

In Example 3, a cartridge for a third cell was formed by spirallywinding around a core tube six membrane pieces, each 100 cm long and 15cm wide, and with six plastic netting spacers (0.010 inch) thick(Netting 4122; Delstar) therebetween. The 12 layers were wound by layingthem on a flat surface one on top of the other in an alternatingpattern, with each membrane separated by a spacer net, and the membraneends offset by 1 cm. A rigid plastic netting tube 15 cm long (RN 2540;Internet, Inc.) was used as the core tube around which the membranes andspacers were wound. After rolling the 12 membrane and spacer layersaround the core tube, the wound assembly was contained with a larger nettube prepared from flat netting (XN 1678, Internet, Inc.). This woundassembly was cut to 13.0 cm in length, and the two end caps wereattached with thermoplastic adhesive. One of the end caps comprised ano-ring to provide a sealed passage for water to flow into and out of thecartridge. The final cartridge with end caps was 13.8 cm tall with an8.9 cm diameter, and comprised 0.78 m² of water-splitting membrane.

A cartridge according to Example 3 was characterized by placing it in acylindrical housing comprising an inner and outer electrode, a centralriser tube as one housing port, and a second port near the top of thehousing's outer wall. The cartridge was first regenerated over 20minutes with water flow in the direction inside to outside (feed waterconductivity was 50 uS/cm), power was limited to a maximum current of0.5 Amps at 250 Volts, and flow rate was 0.1 liters/min to produce a 2liter waste volume (average conductivity of 1750 uS/cm). Forde-ionization, electrode polarity and flow direction were reversed, andfeed water (950 uS/cm) was pumped into the cell at 0.60 liters/minute toproduce 6.4 liters exhibiting 67% TDS reduction. Using the power lawnormalization technique to calculate the volume of water each squaremeter of membrane can treat under these flow and power conditions toprovide 90% R (TDS reduction), one obtains 4.9 liters/m² area for thisdeionization volume for this un-textured membrane.

In Example 4, a cartridge for a fourth cell 102 was fabricated fromtextured membranes 10 having texture features 26 shaped as parallel,spaced apart, ridges 36 and furrows 38, with a d_(pv) (peak to valley)dimensions of about 0.020 cm and d_(pp) (peak to peak) dimensions of0.030 cm. The textured membrane 10 was prepared from the same flat,0.028 cm thick, two-layer membrane sheet used in the previous cell, bypassing this membrane sheet between two metal rolls having the desiredtexture pattern, as shown in FIG. 5. In the texturizing step, the flatmembrane sheet was passed through a short pre-heater to soften themembrane 10, then between the textured rolls themselves, which were alsoheated to a temperature sufficiently high (about 100 C) to impress thetexture pattern into the membrane sheet. The textured membrane sheet wassubsequently swollen in water to provide a textured membrane 10 forspiral winding into a cartridge.

The cartridge in Example 4 was constructed exactly as in Example 3, andcharacterized in the same cell under the identical conditions. Thus themembrane geometric surface area remained 0.78 m². The regeneration watervolume was 2450 uS/cm. The 6.4-liter deionization volume exhibited 90%TDS reduction. Using the power law normalization, this equates to 7.4liters/m² to obtain 90% TDS reduction for this deionization volume usingthis textured membrane.

Thus a 51% improvement in membrane 10 performance was realized for thespiral wound cell of Example 4 which had textured membranes, as comparedto the spiral wound cell of Example 3 which was made from un-texturedmembrane having the same geometric area.

Examples 5 and 6

These examples demonstrate the excellent performance of a cartridgecomprising textured membranes 10 having integral spacers 80, as comparedwith a cartridge having textured membranes 10 that are separated byseparate spacer layers. In Example 5, a cartridge 100 was prepared fromtextured membranes 10 comprising about 50 wt % of weak acid cationexchange resin (HP333 from Rohm and Haas) and strong base anion exchangeresin (SIR100 from Resintech). Six membrane sleeves were constructed,each sleeve being about 85 cm long and 0.064 cm thick, and six 0.0254 cm(10 mil) thick netting spacers were wound and trimmed to a total lengthof 13.8 cm, which was then fitted with end-caps. Thus total membranesurface geometric area was 0.70 m² and the diameter was 8.9 cm. Thecartridge was characterized in an electrochemical cell as described inExamples 3 and 4, to provide 90% TDS reduction from 6.4 liters of asolution stream of water with an initial conductivity of 950 μS/cm. Thepressure drop to provide 0.60-liters/minute-flow rate was 6 psi.

In Example 6, prior to swelling the textured membranes 10 with water, aspacer 80 was formed on the membranes 10 by spraying filaments 82 from athermoplastic spray gun assembly onto the cation exchange layer 14 ofthe membrane 10. The filaments 82 were made with a Pro-Flex Applicationsystem available from Hot Melt Technologies, Michigan. The filaments 82were approximately 50 microns (0.002 inch) in diameter and sprayed in arandom pattern. The spraying process conditions resulted in an integralspacer 80 which rested on top of the texture features 26 of the membrane10, as shown in FIG. 4. Each integral spacer 80 had an average thicknessof about 0.0175 cm (0.007 inch). Eight membrane sleeves each 75 cm longwere wrapped on themselves without the use of separate spacers, thewound membrane trimmed to 13.8 cm, and end-caps applied. The totalmembrane area in the cartridge was 0.83 m² and the diameter was 8.9 cm(19% greater membrane area in the same volume as for Example 5). Thiscartridge was characterized in Example 5 to provide 84% TDS reductionfrom 6.4 liters of challenge water. The pressure drop to provide 0.60liters/minute flow rate was 9 psi.

These results indicate that the integral spacer 80 provide a TDSreduction almost the same as that of the separate spacer between thetextured membranes 10, while reducing the volume of the cartridge byabout 7%. In addition, the integral spacer 80 was found to haveexcellent adherence to the membranes 10, thereby facilitating assemblyof the membranes and spacer layers into a cartridge configuration.

The electrochemical cell of the present invention provides severaladvantages. The surface textured membranes 10 with the integral spacer80 maintains a small, uniform and even gap between the membranes 10,while reducing the overall volume occupied by the electrochemical cell102. Furthermore, the consistent and small gap distances between thetextured membranes 10 with integral spacers 80 reduce current densityvariation and provide consistent mass transport rates and pressure dropsacross the gap between the membranes 10. The textured membranes 10 alsoprovide good ion exchange rates and high solution treatment flow ratesand outputs. Further, the texture features 26 on the membrane 10significantly improve the performance of the membrane to provideunexpected benefits for the membranes 10 and electrochemical cells 102.

The present invention has been described in considerable detail withreference to exemplary versions thereof. However, other versions arealso possible, as would be apparent to one of ordinary skill in the art.For example, other arrangements of membranes in a cartridge, orelectrodes in the electrochemical cell, can also be used depending onthe ion concentration of the solution stream, solution volume to betreated, or ion exchange treatment desired. Further, relative terms,such as first, second, outer, inner, are provided only to illustrate theinvention and are interchangeable with one another, for example, thefirst electrode can be the second electrode. Therefore the spirit andscope of the appended claims should not be limited to the description ofthe preferred versions contained herein.

1. An electrochemical cell comprising: (a) a housing comprising a vesselhaving a solution inlet and a solution outlet, and a detachable lid; (b)a cartridge in the vessel, the cartridge comprising a plurality oftextured bipolar ion exchange membranes abutting one another, eachmembrane having: (i) an anion exchange layer abutting a cation exchangelayer to form a heterogeneous water-splitting interface therebetween,the heterogeneous water-splitting interface comprising continuouscontact between the anion exchange layer and the cation exchange layer;and (ii) an exposed textured surface having a pattern of texturefeatures comprising spaced apart peaks and valleys; and (c) first andsecond electrodes about the cartridge.
 2. An electrochemical cellaccording to claim 1 wherein either: (i) the peaks are ridges and thevalleys comprise furrows between adjacent ridges, the ridges and furrowsbeing generally parallel to a direction that solution travels across themembrane during use of the membrane; or (ii) the peaks comprise conicalprotrusions or mesas, and the peaks extend out from a substantially flatsurface region which defines the valleys.
 3. An electrochemical cellaccording to claim 2 wherein each ridge on the anion exchange layer ofthe membrane lies generally opposite a furrow on the cation exchangelayer.
 4. An electrochemical cell according to claim 1 wherein the peaksand valleys comprise at least one of: (i) a dimension that is greaterthan the thickness of a stagnant layer formed at the membrane surface bya solution traveling across the membrane surface; (ii) a dimension of atleast about 2 microns; (iii) a peak to peak distance d_(pp) of at leastabout 10 microns; (iv) a peak to valley distance d_(pv) of at leastabout 10 microns; (v) an aspect ratio d_(pv)/d_(pp) of at least about0.1; or (vi) an aspect ratio d_(pv)/d_(pp) of at least about
 1. 5. Anelectrochemical cell according to claim 1 comprising an integral spaceron the textured membranes, the integral spacer characterized by at leastone of: (i) filaments on the textured surface; (ii) a coating on thepeaks of the texture features; (iii) a thickness of less than about 1000microns; or (iii) a thickness of less than about 500 microns.
 6. Anelectrochemical cell according to claim 1 wherein the membranes arespirally wound around a core tube.
 7. An electrochemical cell accordingto claim 6 wherein the cartridge comprises end caps and at least one endcap has a hole through which an electrode may pass.
 8. Anelectrochemical cell according to claim 7 wherein both end caps haveO-ring seals.
 9. An electrochemical cell according to claim 1 whereinthe membranes are spirally wound.
 10. An electrochemical cell accordingto claim 1 wherein the membranes are offset from one another by adistance d_(o)=3.14*d_(c)/n, where d_(c) is the outer diameter of a coretube on which the membranes are wrapped.
 11. An electrochemical cellaccording to claim 1 wherein the ends of the membranes are attached toone another.
 12. An electrochemical ion exchange system comprising theelectrochemical cell of claim 1 and further comprising: (a) a powersupply for supplying a voltage to the first and second electrodes; and(b) a pump for flowing a solution stream through the electrochemicalcell.
 13. An electrochemical cell according to claim 1 wherein the endsof the membranes are offset from one another in the same direction. 14.An electrochemical cell according to claim 1 comprising at least one ofthe following: (i) at least one of the first or second electrodescomprises a wire; (ii) a dielectric between the first and secondelectrodes; or (iii) the first and second electrodes comprise titaniumor niobium, and an outer coating of a noble metal.
 15. Anelectrochemical cell according to claim 1 wherein the cartridgecomprises a core tube which slides into a through-hole in the housing toform the solution outlet.
 16. An electrochemical cell according to claim1 wherein the vessel comprises a sidewall and the detachable lidcomprises a plate that is removably attached to the sidewall, the platecomprising a keyhole.
 17. An electrochemical cell according to claim 16wherein the cartridge comprises top and bottom end caps, and the top endcap comprises an end-cap extension which protrudes out and is capable ofextending into the keyhole of the plate, the end-cap extensioncomprising a distal end having an outwardly extending flange.
 18. Anelectrochemical cell according to claim 1 wherein the vessel comprises asidewall having a recessed groove, and the plate of the detachable lidcomprises a side surface having at least a pair of outwardly projectingpins that slide into the recessed groove.
 19. An electrochemical cellaccording to claim 18 wherein the recessed groove comprises a slopedportion with a step-down locking channel so that the detachable lid canbe pushed down and rotated into the step-down locking channel to lockthe lid into the vessel.
 20. An electrochemical cell according to claim1 wherein the surfaces of each of the anion and cation exchange layersat their interface are textured, and the boundary between the anion andcation exchange layers at their water-splitting interface follows thecontour of the textured surfaces.
 21. An electrochemical cell accordingto claim 1 wherein the membranes undulate to form corrugated membranes.22. An electrochemical cell according to claim 1 wherein the pluralityof membranes are arranged to provide a solution passageway that forms aunitary and contiguous solution channel that flows past both the anionexchange layer and the cation exchange layer of each membrane.
 23. Anelectrochemical cell according to claim 22 wherein the unitary channelis connected throughout in an unbroken sequence extending continuouslyfrom the solution inlet to the solution outlet.
 24. A method ofmanufacturing a cartridge for an ion exchange electrochemical cell, themethod comprising: (a) forming a plurality of textured bipolar ionexchange membranes, each membrane having (i) anion and cation ionexchange materials arranged to form a heterogeneous water-splittinginterface comprising continuous contact between the anion exchangematerial and the cation exchange material, and (ii) an exposed texturedsurface having a pattern of texture features comprising peaks andvalleys which are spaced apart from one another; (b) forming an offsetmembrane stack of the textured bipolar membranes which are offset fromone another; (c) providing a core tube and winding the offset membranestack around the core tube to form a cartridge roll; and (d) attachingtop and bottom end caps to the cartridge roll.
 25. A method according toclaim 24 comprising forming membranes with texture features having atleast one of: (i) a dimension greater than the thickness of a stagnantlayer formed at the membrane surface by a solution traveling across themembrane surface; (ii) a dimension of at least about 2 microns; (iii) apeak to peak distance d_(pp) of at least about 10 microns; (iv) a peakto valley distance d_(pv) of at least about 10 microns; (v) an aspectratio d_(pv)/d_(pp) of at least about 0.1; or (vi) an aspect ratiod_(pv)/d_(pp) of at least about
 1. 26. A method according to claim 24wherein (b) comprises laying the membranes on top of one another so thatthe top ends of the membranes are offset from one another in the samedirection.
 27. A method according to claim 26 comprising offsetting thetop ends of the membranes by a distance d_(o)=3.14*d_(c)/n, where d_(c)is the outer diameter of the core tube on which the membranes arewrapped.
 28. A method of forming an electrochemical cell, the methodcomprising providing a electrochemical cell housing having a solutioninlet and a solution outlet, and positioning the cartridge roll formedaccording to claim 27 within the housing such that the core tube isfluidly connected to the solution outlet.
 29. A method according toclaim 26 comprising attaching the top ends of the membranes to oneanother by clips, glue, heat staking, rivets, sewing, staples,ultrasonic bonding or welding.
 30. A method according to claim 24wherein (c) comprises positioning the bottom surface of the offsetmembrane stack on the core tube and winding the membrane stack aroundthe core tube while maintaining a tension on the membrane stack bypulling the membrane stack or applying a radial force.
 31. A methodaccording to claim 24 wherein (b) comprises forming one or moresub-assembly stacks of membranes.
 32. A method according to claim 24wherein (c) further comprises attaching an outer sleeve over thecartridge roll.
 33. A method according to claim 32 comprising attachingthe outer sleeve to the membranes prior to winding, and attaching theouter sleeve to itself with glue, a weld, or a fiber.
 34. A method ofmanufacturing a cartridge for an ion exchange electrochemical cell, themethod comprising: (a) forming a plurality of textured bipolar ionexchange membranes, each membrane having (i) anion and cation ionexchange materials arranged to form a heterogeneous water-splittinginterface comprising continuous contact between the anion exchangematerial and the cation exchange material, and (ii) an exposed texturedsurface having a pattern of texture features comprising peaks andvalleys which are spaced apart from one another; (b) forming an offsetmembrane stack of the textured membranes by laying the membranes on topof one another so that the top ends of the membranes are offset from oneanother in the same direction, and attaching the top ends of the offsetmembranes to one another; (c) providing a core tube and winding theoffset membrane stack around the core tube to form a cartridge roll; (d)wrapping an outer sleeve around the cartridge roll to overlap itself;and (e) applying top and bottom end caps on the cartridge roll.
 35. Amethod of manufacturing a cartridge according to claim 34 comprisingforming the membranes such that either: (i) the peaks are ridges and thevalleys comprise furrows between adjacent ridges, the ridges and furrowsbeing generally parallel to a direction that solution travels across themembranes during use of the membranes; or (ii) the peaks compriseconical protrusions or mesas, and the peaks extend out from asubstantially flat surface region which defines the valleys.
 36. Amethod of manufacturing a cartridge according to claim 34 comprisingforming the membranes such that the peaks and valleys comprise at leastone of: (i) a dimension that is greater than the thickness of a stagnantlayer formed at a membrane surface by a solution traveling across themembrane surface; (ii) a dimension of at least about 2 microns; (iii) apeak to peak distance d_(pp) of at least about 10 microns; (iv) a peakto valley distance d_(pv) of at least about 10 microns; (v) an aspectratio d_(pv)/d_(pp) of at least about 0.1; or (vi) an aspect ratiod_(pv)/d_(pp) of at least about
 1. 37. A method of manufacturing acartridge according to claim 34 comprising winding the membranes in aspiral around the core tube.
 38. A method of manufacturing a cartridgeaccording to claim 34 comprising offsetting the membranes from oneanother by a distance d_(o)=3.14*d_(c)/n, where d_(c) is the outerdiameter of the core tube on which the membranes are wrapped.
 39. Amethod of manufacturing a cartridge according to claim 34 comprisingforming the offset membrane stack such that the plurality of membranesare arranged to provide a solution passageway that forms a unitary andcontiguous solution channel that flows past both the anion exchangematerial and the cation exchange material of each membrane.
 40. A methodof forming an electrochemical cell, the method comprising: (a) providinga housing having a solution inlet and a solution outlet; (b) forming acartridge by: (1) forming a membrane stack by laying textured bipolarion exchange membranes on top of one another so that the top ends of themembranes are offset from one another in the same direction, andattaching the top ends of the offset membranes to one another, eachtextured bipolar ion exchange membrane having an anion exchange layerabutting a cation exchange layer to form (i) a heterogeneouswater-splitting interface comprising continuous contact between theanion exchange layer and the cation exchange layer, and (ii) an exposedtextured surface; (2) providing a core tube and winding the offsetmembrane stack around the core tube to form a cartridge roll; and (3)applying top and bottom end caps on the ends of the cartridge roll; and(c) positioning the cartridge roll within the housing so that the coretube is fluidly connected to the solution outlet of the housing.
 41. Amethod of forming an electrochemical cell according to claim 40comprising forming the membranes such that each membrane has an exposedtextured surface having a pattern of texture features comprising peaksand valleys which are spaced apart from one another and either: (i) thepeaks are ridges and the valleys comprise furrows between adjacentridges, the ridges and furrows being generally parallel to a directionthat solution travels across the membranes during use of the membranes;or (ii) the peaks comprise conical protrusions or mesas, and the peaksextend out from a substantially flat surface region which defines thevalleys.
 42. A method of forming an electrochemical cell according toclaim 40 comprising forming membranes such that each membrane has anexposed textured surface having a pattern of texture features comprisingpeaks and valleys which are spaced apart from one another, the peaks andvalleys comprising at least one of: (i) a dimension that is greater thanthe thickness of a stagnant layer formed at the membrane surface by asolution traveling across the membrane surface; (ii) a dimension of atleast about 2 microns; (iii) a peak to peak distance d_(pp) of at leastabout 10 microns; (iv) a peak to valley distance d_(pv) of at leastabout 10 microns; (v) an aspect ratio d_(pv)/d_(pp) of at least about0.1; or (vi) an aspect ratio d_(pv)/d_(pp) of at least about
 1. 43. Amethod of forming an electrochemical cell according to claim 40comprising winding membranes in a spiral around the core tube.
 44. Amethod of forming an electrochemical cell according to claim 40comprising offsetting the membranes from one another by a distanced_(o)=3.14*d_(c)/n, where d_(c) is the outer diameter of the core tubeon which the membranes are wrapped.
 45. A method of forming anelectrochemical cell according to claim 40 comprising forming themembrane stack such that the plurality of membranes are arranged toprovide a solution passageway that forms a unitary and contiguoussolution channel that flows past both the anion exchange layer and thecation exchange layer of each membrane.
 46. A housing for anelectrochemical ion exchange cell comprising a cartridge having anend-cap extension with a flange, the housing comprising: (a) a vesselhaving a sidewall connected to a bottom wall, a solution inlet, and asolution outlet; and (b) a detachable lid that can be removably attachedto the sidewall of the vessel, the detachable lid comprising a platehaving a keyhole that extends therethrough, the keyhole comprising afirst hole having a dimension larger than the end-cap extension, and asecond hole which opens into the first hole, the second hole having adimension smaller than the flange of the end-cap extension.
 47. Ahousing according to claim 46 wherein the keyhole comprises a first holethat is circular and a second hole that is an elongated aperture with asemicircular end.
 48. A housing according to claim 46 wherein the platecomprises a side surface having a thread for screwing into a receivingthread in the sidewall of the vessel.
 49. A housing according to claim46 wherein the plate comprises a handle which assists an operator inscrewing the lid.
 50. An electrochemical cell comprising the housing ofclaim 46, and further comprising a cartridge having a plurality ofspiral wrapped membranes, the membranes having a textured surface, andelectrodes about the membranes.
 51. A housing for an electrochemical ionexchange cell comprising a cartridge having an end-cap extension, thehousing comprising: (a) a vessel having a sidewall connected to a bottomwall, a solution inlet, and a solution outlet; and (b) a detachable lidthat can be removably attached to the sidewall of the vessel, thedetachable lid comprising a plate with a hollow post extending outwardlytherefrom, the hollow post sized to slide into or over the end-capextension of the cartridge of the electrochemical cell.
 52. A housingaccording to claim 51 further comprising a groove about the base of thehollow post and an O-ring in the groove.
 53. A housing according toclaim 51 wherein the plate comprises a side surface having a pluralityof pins extending outwardly therefrom, the pins sized to fit into arecessed groove in the sidewall of the vessel.